Lactating females and certain adult males form conspicuous nonsexual relationships, friendships, shortly after parturition. Although well studied, the adaptive significance of friendship for females remains unclear. We tested the alternative hypotheses that male friends protect females from intrasexual harassment from higher-ranking females versus intersexual coercion from other males. These hypotheses make contrasting predictions about the adrenocortical profiles of lactating females. Fecal samples and observational data on social behavior and spatial relations were collected from 26 adult males and 22 lactating females. Fecal glucocorticoid metabolites were assessed by corticosterone radioimmunoassay on field-extracted hormones. Friendships were determined from composite proximity scores (C-scores) calculated for each male-female dyad in the groups. There were three key results. Basal glucocorticoid levels were significantly lower in lactating females who had at least one high-ranking male friend than in those who had only low-ranking male friends [Mann-Whitney U Test: U=30.0, n1=13, n2=3, p<0.05]. Females (both high and low-ranking) who were more responsible than their male friends for maintaining friendships (measured by Hinde’s Index) had significantly higher glucocorticoid levels [Mann-Whitney U Test: U=27.0, n1=13, n2=3, p<0.05]. These findings are consistent with the “male-harassment” hypothesis. There was no association between female rank and glucocorticoid levels [Mann-Whitney U Test: U=41.0, n1=7, n2=9, p=0.23]